Initially, the word stress was loosely borrowed from physics. Humans, it was thought, are in some ways similar to physical objects such as metals, which resist moderate outside forces but lose their resiliency under greater pressure. But, unlike metals, human beings can think and reason, and they experience a myriad of social and environmental circumstances that make defining stress more complex in psychology than in physics. Thus, in psychological terms, we can define stress as the response of individuals to stressors, the circumstances and events that threaten them and tax their coping abilities.